1. Field of the Invention
The present invention is directed to improved sorption cooling devices and to temperature-controlled shipping containers incorporating the cooling devices. In particular, the present invention is directed to sorption cooling devices that are adapted to maintain a reduced temperature within an enclosed container for an extended period of time. The devices are particularly useful for temperature-controlled shipping containers that must maintain a temperature below ambient for extended time periods such as 24 to 72 hours.
2. Description of Related Art
The shipment of products that must have their temperature maintained within a specific range below ambient is one of the fastest growing market segments in the modern shipping industry. This growth is driven by a number of factors including widespread concerns about safety in the cold food distribution chain, increasing numbers of pharmaceutical and life sciences products which must have their temperature maintained within certain limits, the rapid growth in high-value specialty chemicals such as those used in the semiconductor industry, the increasing number of sophisticated medical tests which require the shipment of patient specimens to an external laboratory, the increased number of clinical trials associated with new pharmaceutical discovery and the increased delivery of products directly to the customer as a result of Internet ordering.
This field is generally referred to as controlled temperature packaging (CTP). CTP can be segmented by the target temperature range, namely: frozen (below 0xc2x0 C.); 2xc2x0 to 8xc2x0 C., and less than ambient (e.g., less than 30xc2x0 C.). In addition, CTP may be segmented by container size, namely: greater than pallet; one cubic foot to pallet; and less than one cubic foot. Containers having a size greater than pallet are typically cooled by mechanical refrigeration and the shipment times are typically from days to many weeks. The one cubic foot to pallet size segment is dominated by systems using ice (e.g., gel packs) and/or dry ice as a coolant wherein the containers are insulated using expanded polystyrene (EPS). The market segment for containers less than one cubic foot in size is very limited due to an unmet need for a small, lightweight cooling mechanism.
Although many basic ice/EPS systems are in use, there is a wide variation in quality and performance of the packaging depending on the value of the product and the sensitivity of the product to temperature fluctuation. A relatively simple system includes a cardboard box into which EPS sheet has been cut and placed. The container is then filled with dry ice in which, for example, frozen fish is shipped. A more sophisticated approach is a validated system consisting of custom molded EPS forms in a rigid box with both frozen and warm gel packs, the combination of which has been tested through a range of temperature cycles for specified thermal properties. Such a validated system can be used for shipping pharmaceuticals. For example, many pharmaceutical products such as vaccines and antibodies must be maintained at 2xc2x0 C. to 8xc2x0 C.
The existing ice/EPS cooling system is unsatisfactory because of increased environmental concerns associated with disposal of large quantities of EPS and gel packs with the high cost of shipping. Gel packs also require freezers at the shipping source to maintain the frozen packs. The high cost of shipping is directly related to the high volume associated with the EPS and the high volume and mass associated with the gel packs. As an example, for a one cubic foot box with a 60 hour lifetime at 2xc2x0 C. to 8xc2x0 C., over 90 percent of the volume is consumed by EPS and gel packs. Some reduction in volume and shipping costs may be obtained by using vacuum insulation panels (VIPS), but the high cost of VIPs has precluded significant market penetration.
An example of the foregoing system is illustrated in U.S. Pat. No. 5,924,302 by Derifield issued on Jul. 20, 1999. This patent illustrates a shipping container that includes a plurality of cavities adapted to receive a coolant (e.g., gel packs) that surround a cavity adapted to receive an item to be shipped.
Electrically cooled shipping containers are also known, as illustrated in U.S. Pat. No. 6,192,703 by Salyer et al. issued on Feb. 27, 2001. This patent discloses a portable refrigerator unit and storage container employing vacuum insulation panels and a phase change material. Phase change materials undergo a change in physical form (e.g., solid to liquid) thereby absorbing heat from the surrounding environment. A battery driven refrigeration system provides cooling of the shipping container.
There is a need for a temperature-controlled container, such as a shipping container, having a lightweight cooling mechanism that does not occupy a large volume. It would be advantageous if the temperature of the container was controllable over a range of temperatures. It would also be advantageous if the cooling mechanism had the ability to maintain the reduced temperature for an extended period of time.
The present invention is generally directed to sorption cooling devices. The sorption cooling devices are particularly useful for controlled temperature shipping containers.
According to one embodiment of the present invention, a sorption cooling device is provided. The sorption cooling device includes an evaporator, an absorber, at least a first reservoir adapted to contain a liquid and a liquid disposed in the first reservoir. Flow restriction means is disposed between the liquid and the evaporator for restricting the flow of the liquid to the evaporator, thereby providing cooling at a controlled rate.
According to another embodiment of the present invention, a sorption cooling device is provided that includes an evaporator, an absorber, at least a first reservoir adapted to contain a first liquid and at least a second reservoir adapted to contain a second liquid. Means for supplying liquid from the first and second reservoirs to the evaporator is also provided wherein the first reservoir supplies liquid to the evaporator at a rate faster than the liquid supply rate from the second reservoir. For example, flow restriction means can be disposed between the liquid and the evaporator for restricting the flow of the liquid from the second reservoir to the evaporator.
According to another embodiment of the present invention, a method is provided for operating a sorption cooling device having an evaporator for providing cooling and an absorber for absorbing vapor formed in the evaporator. A first portion of liquid is supplied to the evaporator at a first liquid supply rate and a second portion of liquid is supplied to the evaporator at a second liquid supply rate that is lower than the first liquid supply rate. This method advantageously enables rapid initial cooling and subsequent controlled maintenance of the cooling over an extended period of time.
According to another embodiment, a sorption cooling device is provided that includes an evaporator, an absorber and a vapor conduit connecting the evaporator and the absorber. The vapor conduit comprises a thermally insulating material such as an open cell foam to reduce the heat transfer between the evaporator and absorber while permitting vapor flow therethrough.
According to yet another embodiment, a sorption cooling device is provided that includes an absorber, an evaporator and a reservoir adapted to supply a liquid to the evaporator. A freezing point suppression agent is dispersed within the evaporator to reduce freezing of the liquid in the evaporator.